1. Field of the Invention
The invention relates to a relay driving module, more particularly a relay driving module for driving a latching relay with a limited amount of current.
2. Description of the Related Art
A relay is normally used as a switch, e.g., a power switch, in an electronic device. A latching relay consumes power only during switching between an on state and an off state (also referred to as a reset state).
With reference to FIG. 1, U.S. Pat. No. 5,079,667 discloses a conventional relay driving circuit that includes an input voltage level detector 81, a set switch 84, a relay 85, and a reset switch 86. The input voltage level detector 81 detects an input voltage (Vin) at an input side, and turns on the set switch 84 when the input voltage (Vin) is greater than a threshold value so as to provide a set current for driving the relay 85 to turn on. On the other hand, when the input voltage (Vin) is smaller than the threshold value, the input voltage level detector 81 turns on the reset switch 86 so as to turn off the relay 85.
With reference to FIG. 2, U.S. Pat. No. 4,418,374 discloses another conventional relay driving circuit that includes a resistor 93 across an input side, a capacitor 94, a programmable controller 95, a relay including a set inductor 97, and first and second switches 96, 99. As the input voltage (Vin) across the resistor 93 increases, and the capacitor 94 is charged. When the voltage across the resistor 93 exceeds a reference voltage provided by the programmable controller 95, the programmable controller 95 turns on the first switch 96 such that the voltage across the resistor 93 is couple to the set inductor 97 for turning on the relay. On the other hand, when the input voltage (Vin) is lower than the reference voltage, the programmable controller 95 turns off the first switch 96, and turns on the second switch 99, such that the capacitor 94 discharges through the reset inductor 90 and the second switch 99, thereby turning off the relay.
Furthermore, as shown in FIG. 3, a conventional power supply system for a liquid crystal display operates as follows. When the liquid crystal display operates under an operating mode, a power supplying member 71 supplies power to a control circuit 72 and a liquid crystal display panel 73 for normal operations, where the control circuit 72 transmits a display signal to the liquid crystal display panel 73 for image display thereby. When the liquid crystal display enters a power saving mode, power is no longer supplied to the liquid crystal display panel 73, but is still supplied to the control circuit 72 such that the control circuit 72 can switch back to the operating mode at any time upon receipt of the display signal. In other words, under the power saving mode, the power supplying member 71 still needs to supply power to the control circuit 72, resulting in continuous consumption of power that accumulates to a significant amount in the long run.